3 ms·

> I once asked the infamous 'how man tennis balls on a 747' question - and the interviewee started calculating how many balls would fit in the area of various b

> I once asked the infamous 'how man tennis balls on a 747' question - and the interviewee started calculating how many balls would fit in the area of various body parts, it was ridiculous. I guess the implication here is that this was a bad approach? This is why I would be skeptical of this sort of question, it's really not clear to me why you think that answer is any more ridiculous than the question.

sonnyblarney 8y ago
Because the question is entirely reasonable. In fact, to the extent that it's novel to the candidate and they haven't heard it before - it's an excellent question. It requires someone to actually think a little bit, to reason about an unknown scenario, and to try to apply intelligence to an otherwise undiscovered set of variables. Do they know the formula for the volume of a sphere? Will they consider how balls might fit in a lattice? Can they estimate how many balls fit in a cubic meter? Can they reason about how large a plane actually is? Can they even do basic math? Can they make rough estimates, piece everything together and come up with a rough estimate? Can they parameterize the estimate? There are any number of tangents to move along and consider. Watching someone answer this question can tell you quite a lot about how they think, reason and communicate. There are nary any circumstances in business that have clear data points, clear outcomes, or perfectly clear objectives and unfortunately, our current interviewing paradigms generally don't account for that. The best question I was ever asked was during a McKinsey interview: "it's 1965, Sweden is going to switch from driving on the left, to the right side of the road, you have 2 years until this day, how do you plan it?" ... which leads to some amazing discussions. It's definitely a good consulting question.
- crdrost 8y ago
  I guess I'd reply after some consideration that what I think is unreasonable about this question is just that I as a physicist know exactly how to answer it because I have received years of training in reasoning about things that I don't know and years of understanding error bars and orders of magnitude, so that I can say "well within a half-order it's this." But I came to know a lot of professional mathematicians in that time, and they are people with very big minds, extraordinarily creative -- but several of them would potentially struggle on these sorts of questions (indeed some of them would struggle with arithmetic, having long since just unloaded that burden onto calculators and computers to free their brain for more interesting thoughts) simply because they're not used to reasoning about uncertainty. They are likely to simultaneously be very good hires, and to only give you the barest of lower bounds. "I mean, it's at least 30 because I can fit 30 in a carry-on. Oh, but there could be a hundred seats and a hundred carry-ons, so I guess it's at least 3000." "It's, uh, it's way more than that." "Right, I said 'at least'. I mean we could probably stuff at least two carry-ons in each seat, so that gets us towards a better lower bound of 9000 or 10,000?" "Yeah, uh, still much much more." I know other folks who would make great junior or mid-level developers who never had any formal education and wouldn't be comfortable approaching this either from the "let me look up or estimate volumes and recall packing densities" or the "I can give you lower bounds based on the things I am absolutely sure about" approaches. They wouldn't necessarily know, for example, that one might just say "okay let me look up the size of a 747" in an interview, that such a thing is probably "within the rules" of what the question expects -- unless prompted, and even then. Let me put this a different way, do you think that responses to that question could be improved if before the interview you walked a candidate through a similar problem for ten minutes? Because I would imagine it could be, but maybe you ask it in a way that already provides for that. The problem is that if people can do substantially better with a ten-minute nudge then you are actually just testing for who has already had the sort of life experience to give them that ten-minute nudge, and that doesn't seem like an "excellent question" to me.

sonnyblarney 8y ago

Because the question is entirely reasonable. In fact, to the extent that it's novel to the candidate and they haven't heard it before - it's an excellent question. It requires someone to actually think a little bit, to reason about an unknown scenario, and to try to apply intelligence to an otherwise undiscovered set of variables. Do they know the formula for the volume of a sphere? Will they consider how balls might fit in a lattice? Can they estimate how many balls fit in a cubic meter? Can they reason about how large a plane actually is? Can they even do basic math? Can they make rough estimates, piece everything together and come up with a rough estimate? Can they parameterize the estimate? There are any number of tangents to move along and consider. Watching someone answer this question can tell you quite a lot about how they think, reason and communicate. There are nary any circumstances in business that have clear data points, clear outcomes, or perfectly clear objectives and unfortunately, our current interviewing paradigms generally don't account for that. The best question I was ever asked was during a McKinsey interview: "it's 1965, Sweden is going to switch from driving on the left, to the right side of the road, you have 2 years until this day, how do you plan it?" ... which leads to some amazing discussions. It's definitely a good consulting question.

crdrost 8y ago
I guess I'd reply after some consideration that what I think is unreasonable about this question is just that I as a physicist know exactly how to answer it because I have received years of training in reasoning about things that I don't know and years of understanding error bars and orders of magnitude, so that I can say "well within a half-order it's this." But I came to know a lot of professional mathematicians in that time, and they are people with very big minds, extraordinarily creative -- but several of them would potentially struggle on these sorts of questions (indeed some of them would struggle with arithmetic, having long since just unloaded that burden onto calculators and computers to free their brain for more interesting thoughts) simply because they're not used to reasoning about uncertainty. They are likely to simultaneously be very good hires, and to only give you the barest of lower bounds. "I mean, it's at least 30 because I can fit 30 in a carry-on. Oh, but there could be a hundred seats and a hundred carry-ons, so I guess it's at least 3000." "It's, uh, it's way more than that." "Right, I said 'at least'. I mean we could probably stuff at least two carry-ons in each seat, so that gets us towards a better lower bound of 9000 or 10,000?" "Yeah, uh, still much much more." I know other folks who would make great junior or mid-level developers who never had any formal education and wouldn't be comfortable approaching this either from the "let me look up or estimate volumes and recall packing densities" or the "I can give you lower bounds based on the things I am absolutely sure about" approaches. They wouldn't necessarily know, for example, that one might just say "okay let me look up the size of a 747" in an interview, that such a thing is probably "within the rules" of what the question expects -- unless prompted, and even then. Let me put this a different way, do you think that responses to that question could be improved if before the interview you walked a candidate through a similar problem for ten minutes? Because I would imagine it could be, but maybe you ask it in a way that already provides for that. The problem is that if people can do substantially better with a ten-minute nudge then you are actually just testing for who has already had the sort of life experience to give them that ten-minute nudge, and that doesn't seem like an "excellent question" to me.